The present invention relates generally to a sports shoe or boot, such as a football shoe or boot or the like, including an outer sole comprising resiliently flexible plastic material, and projections such as studs or bars comprising a wear-resistant plastic material, on the sole. For the sake of simplicity herein, the term sports shoe will be used to cover any appropriate form of sports shoe, sports boot (being generally of a heavier construction than a sports shoe in the narrow sense) and the like.
Sports shoes having gripping projections on the underneath of the sole thereof are generally particularly intended for use in field-type sports, such as football and the like. One such form of sports shoe may have calks or studs of comparatively hard material, for example polyamide, which are replaceably secured to the sole. The shoe usually has a comparatively small number of such projections (for example, up to six or eight projections). Alternatively, a sports shoe may be provided with a larger number (for example up to around 20) of studs or projections which are normally formed by casting or moulding integrally with the sole. The material used for the projections and thus for the sole is comparatively soft and yielding, in order to give greater resiliency in contact with the ground. The present invention is more particularly concerned with sports shoes of the second kind referred to above. Such sports shoes are advantageous over the first-mentioned shoes or boots which have replaceable studs or the like, insofar as the larger number of projections and the more pronounced flexibility and resiliency of the material used for the sole mean that contact between the shoe and the ground is more uniform, giving rise to a more even spread of the loading applied by the body of the person wearing the shoe, while also imparting a certain degree of flexibility or compliance to the sole of the boot or shoe, which also contributes to making the boot or shoe more comfortable to wear in particular on hard ground such as on frozen sports fields and the like. For that reason, boots or shoes of that kind are used in particular as training shoes by footballers.
However, a disadvantage of sports shoes or boots of the above-discussed kind, wherein the sole and the studs or projections thereon are formed integrally from the same material is that the material which desirably experiences resilient deformation under pressure, to provide greater comfort in wearing the boot or shoe, is susceptible to a comparatively high rate of wear. Therefore, either the soles and the projections must all be made from high-strength and therefore expensive plastic materials, or alternatively the studs or projections must be made from a different material from the material for the sole, which therefore has a considerably higher degree of resistance to wear, with the projections possibly being replaceable, in a similar manner to the studs of the first kind of boot or shoe referred to above (see for example the constructions disclosed in German Utility Model No 18 99 723 or French patent specification No 2 070 253). However, the constructions set forth in the documents just mentioned have not been successful under practical circumstances because the projections, made from the wear-resistant material, are comparatively unyielding and therefore a shoe constructed in that manner loses a substantial part of its shock-absorbing properties or, if the projections are formed merely by a comparatively thin shell of the high-strength material referred to above, which is screwed on to screwthreaded projections on the underneath of the sole, the shells nonetheless suffer from wear at a relatively high rate. In this connection, there is then even the danger that the screwthreaded fittings on the underneath of the sole themselves suffer damage so that the sports shoe is rendered useless as a result.